Floating-brush contact assembly



Jan. 10, 1967 G. E. WENDELL 3,297,973

FLOATINGBRUSH CONTACT AS S EMBLY Filed Aug. 50, 1963 2 Sheets-Sheet lGeo/ye a. [Jan/2% Jan. 10, 1967 G. E. WENDELL FLOATING-BRUSH CONTACTASSEMBLY 2 Sheets-Sheet 2 Filed Aug. 50, 1965 United States Pate3,297,973 FLOATING-BRUSH CONTACT ASSEMBLY George E. Wendell, Blacksburg,Va., assignor to Poly- Scientific Corporation, Blacksburg, Va. FiledAug. 30, 1963, Ser. No. 305,760 11 Claims. (Cl. 339) This inventionrelates to sliding or rotating contact assemblies, and, moreparticularly, to contact assemblies in which very light contactingpressures are employed.

A great deal of study has gone into the mechanism of electric conductionbetween two relatively movable conductors. Despite this extensive workand the many prior constructions which have been proposed, a number ofsignificant problems remain. Initially, contact life and the reliabilityof conduction over long periods of time are not as high as would bedesirable. This problem is attributable, at least in part, to the commonuse of high contact pressures, and to the presence of harmful organicvapors which tend to attack the contacting surfaces and increase theirresistance. The organic vapors are frequently a result of soldering orpotting operations which occur when the relatively movable contacts areassembled.

Accordingly, principal objects of the present invention includereduction in the contact pressure of moving electrical contacts andelimination of the need for soldering and potting at the time thecontacting assemblies are manufactured.

In the case of multiple contacts, such as those found in brush blockassemblies, where as many as 20 or 30 or more brushes engagecorresponding commutator or slipring elements, it is frequentlydifi'icult to assemble or disassemble the units or to replace brushes.Furthermore, the alignment and adjustment of contact pressures is aserious problem in the tiny space which is allocated to each brushwithin the brush block assembly.

Another object is the simplification of assembly and replacement ofbrushes without contamination of the contacting surfaces.

In accordance with the present invention, the foregoing objects areachieved by the use of a piece of conductive wire having a bend alongits length, a conducting tube into which the bent wire fits loosely, anda grooved conductor, such as a slip-ring or commutator, which is engagedtangentially by the Wire.

In a preferred embodiment of the invention, four separate bentconductive Wires are loosely inserted in a single conductive tube, adoubly grooved slip-ring is provided, two of the wires engage separategrooves in one direction from the tube; and the two remaining wires facein the other direction and tangentially engage the same two grooves atpoints spaced around the periphery of the slipring from the points ofengagement of the first two wires.

One of the important features of the construction described above isthat the individual wires are free to rotate about the axis of theconductive tube in which they are inserted. This permits a relief ofstrain and a free-floating contact relationship between the wires andthe groove or grooves.

With this arrangement, automatic alignment is achieved and contactpressure may be reduced from the normal pressure of four or five gramsdown to one or two grams, or even less. The assembly, disassembly andcleaning, and the replacement of brushes may be accomplished in a cleanroom with no soldering, potting or other source of noxious vaporspresent which could contaminate or corrode the moving contact surfaces.

Other advantages of the present construction involve a greater range ofselection of brush materials, since soldering or welding to the wirebrush is eliminated, a reduction in size of brush block assemblies,simplified construction, lower costs, and increased product reliability.

Patented Jan. 10, 1967 tice The novel features which are believed to becharacteristic of the invention, both as to its organization and methodof operation, together with further objects and advantages thereof, willbe better understood from the following description considered inconnection with the accompanying drawings in which several embodimentsof the invention are illustrated by way of example. It is to beexpressly understood, however, that the drawings are for the purpose ofillustration and description only, and are not intended as a definitionof the limits of the invention.

In the drawings:

FIG. 1 is a schematic view of a brush and slip-ring contact assemblyshown in partial cross-section, in accordance with the invention;

FIG. 2 is a cross-sectional view taken along lines 2-2 of FIG. 1;

FIG. 3 is an enlarged view of a portion of the contact assembly of FIG.2;

FIG. 4 is a partial cross-sectional view taken at right angles to FIG.3; and

FIG. 5 is a cross-sectional view taken along lines 55 of FIG. 3.

With reference to the drawings, FIG. 1 shows a brush block aassemblyincluding an inner subassembly 12 having a set of grooved conductingrings, and an outer subassembly 14 including many sets of brushes. Theactive elements of the brush subassembly are the wires 16 which engagethe grooved conducting rings in the assembly 12. Other components shownin FIG. 1 include the outer housing 18, the brush leads 20 and theslip-ring leads 22. The slip-ring assembly 12 is mounted on ballbearings 24 and 26 for relative movement with respect to the electricalbrush assembly 14.

In practice, either the brush assembly 14 or the slipring assembly 12may be fixed while the other rotates. The leads 20 are connected to theconductive sleeves 28 which hold the wires 16v The leads 22 are pottedwithin an insulating core inside the slip-ring assembly 12 and arebrought out through the cylindrical member 30 which is secured to theright-hand end of slip-ring assembly 12, as shown in FIG. 1.

FIG. 2 is a cross-sectional view taken along lines 2-2 of FIG. 1. Itshows the relative positions of the brush assembly 14 and the slip-ringassembly 12 to advantage.

FIG. 3 is an enlarged view of a portion of FIG. 2 showing the precisearrangement of the brush wires 16 and the slip-rings of assembly 12. Asclearly shown in FIGS. 2 and 3, the wires 20 pass through the insulatingcylinder 32 and are soldered to the sleeve 28. The wires 16 are bent andslip freely into the conducting sleeves 28. The wires 16 are bent andslip freely into the conducting sleeves 28. The slip-ring assembly 12 isprovided with a series of conductive rings including the ring 34 shownin FIGS. 2 and 3. These rings are spaced and insulated from one another.One of the leads 22 is connected to slipring 34.

Other views of wires 16 and their engagement with the doubly groovedslip-ring 34 are shown in FIGS. 4 and 5. Thus, FIG. 4 shows a view ofthe wires 16 which is taken at right angles from the view of FIG. 3.Similarly, FIG. 5 is a partial cross-sectional view taken along lines5-5 of FIG. 3.

The wires 16 are held in the conductive tube 28 solely by the pressureexerted against the tube 28 and the tangential pressure againstslip-ring 34. This permits free rotation of each of the wires 16 aboutthe axis of tube 28 and therefore secures precise alignment of the wirein the grooves of slip-ring 34. In actual practice, the wires 16 arepreformed and bent to a precise angle before insertion onto tube 28.

In one particular case, a wire of an alloy known as Paliney-7 wasmounted in a brush block assembly having an inner diameter of 0.170 inchto run on a slip-ring having an outer diameter of 0.122 inch. The wirehad a diameter of 0.0027 inch. In order to obtain a two-gram pressure onthe commutator, the wire was initially bent to tangentially engage acylinder having a diameter of 0.106 inch. For completeness, it may benoted that the alloy Paliney-7 has a composition of 10 percent gold, 10percent platinum, 35 percent palladium, 30 percent silver, 14 percentcopper and 1 percent zinc.

In each case, the contact pressure is determined as a function of themechanical properties of the contact wire, and the geometry of theassembly. Normally, for miniature sizes, contact pressures will begreater than one-tenth gram and less than the usual four or five gramsemployed in prior devices of the same genera-l size, and wouldcharacteristically be one or two grams. For larger size brushes, heavierpressures would be employed; in the normal case, however, contactpressures in arrangements fabricated in accordance with the inventionwill be a fraction of that of prior art units of comparable size.

With regard to another aspect of the present invention, it has beendetermined that brushes and commutators of the same material mayactually be employed without adverse effects. Thus, a slip-ring platedwith gold was successfully employed with a wire brush having gold platedonto beryllium copper wire. This experiment was considered to beparticularly interesting and indicative of the advantages of the presentinvention in view of the fact that it is contrary to most of the knownprinciples in the field of sliding contacts to use both brushes andsliprings or commutators of the same material. In most cases, suchcontact surfaces are rapidly degraded through galling and fail withinshort periods of time. However, with the lack of contamination and therelatively light pressure, life-times equal or superior to normalcontact wear was achieved even with identical metal surfaces.

Concerning material which may be used, Neoro-28A, a high gold alloy, andNeoro-G wire have been successfully employed. Neoro-ZSA includes 75percent gold, 22 percent silver, and 3 percent nickel. Neoro-G includes72% percent gold, 4 percent silver, 1 percent zinc, 8 /2 percentplatinum and 14 percent copper. Coin gold, including 10 percent copperand 90 percent gold, and other known precious metal contact materialsmay also be employed. With any of the foregoing materials, it hasuniformly been found that the use of brush and slip-ring or commutatorassemblies in accordance with the present invention produces much longercontact life and greater reliability than arrangements which have beenproposed heretofore employing the same or comparable materials.

In closing, advantages of the present invention include reduction in therequired torque for driving the commutator, and the other advantagesmentioned above. Some of these advantages which were previouslydiscussed include simplification of construction, ease of assembly andbrush replacement, reduction in cost, redundancy of contacts in the caseof the multiple wire slip-ring units, reduction in size of the over-allassembly, a greater range of selection of brush materials, and greatlyincreased reliability and contact life.

It is to be understood that the above-described arrangementsareillustrative of the application of the principles of the invention.Numerous other arrangements within the scope of the invention may bedevised by those skilled in the art. Thus, by way of example and not oflimitation, one, two or six br-ushes could be employed instead of thefour brushes used in the preferred embodiment of the invention; thegrooved conductive rings may .be segmented to form commutators andemployed with brushes extending in but one direction; linear relativemovement of brushes and matching grooved surfaces may be employed withcurved wire brushes; and materials other than those specified could alsobe used. Accordingly, from the foregoing, it is evident that variouschanges may be made in the present invention without departing from thespirit of the invention as defined in the appended claims.

What is claimed is:

1. In combination:

a brush assembly comprising a hollow conductive tube and four bent wireseach having one end extending loosely into said tube; and

a doubly grooved slip-ring mounted for relative rotation with respect tosaid brush assembly, two of said wires engaging respective grooves inthe slip-ring in one direction from said conductive tube, and the othertwo wires engaging the respective grooves in the other direction fromsaid tube.

2. In combination:

a brush assembly comprising a hollow conductive tube and four bent wireseach having one end extending loosely into said tube; and

a doubly grooved slip-ring mounted for relative rotation with respect tosaid brush assembly, two of said wires tangentially engaging respectivegrooves in the slip-ring in one direction from said conductive tube, andthe other two wires tangentially engaging the respective grooves in theother direction from said tube.

3. In a floating brush contact arrangement:

a brush assembly comprising a plurality of hollow conductive tubes;

four bent wires associated with each tube, each wire having one endextending loosely into each of said tubes; and

a corresponding plurality of doubly grooved slip-rings mounted forrelative rotation with respect to said brush assembly, two of the wiresin each set engaging respective grooves in one of the slip-rings in onedirection from each of said conductive tubes, and the two other wiresengaging the respective grooves in the other direction from said tube.

4. In combination:

a brush assembly comprising a hollow conductive tube and four bent wireseach having one end extending loosely into said tube, and a doublygrooved slipring mounted for relative rotation with respect to saidbrush assembly; and

two of said wires engaging respective grooves in the slip-ring in onedirection from said conductive tube, and the other two wires engagingthe respective grooves in the other direction from said tube with lessthan four grams of pressure.

5. In combination:

a brush assembly comprising a plurality of hollow conductive tubes;

a set of four bent wires associated with each tube, each wire having oneend extending loosely into each of said tubes; and

a corresponding plurality of doubly grooved conductors mounted forrelative movement with respect to said brush assembly, two of the wiresin each set tangentially engaging respective grooves in one of theconductors in one direction from each of said conductive tubes, and thetwo other wires of the same set tangentially engaging the respectivegrooves of the same conductor in the other direction from said tube.

6. In a rotary contact assembly,

a brush support,

a ring having a conductive surface mounted for relative rotationalmovement with respect to the brush support,

said brush support having means defining an elongated openingconfronting the ring and containing an electrically conductive meanspermitting angular movement of the brush and making electrical contactwith the brush for all angular positions thereof,

a resilient electrically conductive brush with one end thereof having asubstantially straight portion, said brush being of smaller dimensionthan said opening and inserted loosely into said opening in the brushassembly and in electrical engagement with said conductive means,

said brush having a bend along its length, with said one end thereof onone side of the bend,

means for limiting the penttration of the brush into said opening,

a portion of the brush on the other side of the bend tangential-1yengaging the ring,

the respective size of said opening and said brush, and

the location of said opening in the brush support relative to thesurface of the ring being such that the brush is maintained incontinuous contact with the conductive means in the brush support andwith the ring solely by the opposing pressures on the brush exerted bythe ring and the brush support,

whereby the brush is free to shift angular position in the brush supportand maintain continuous alignment with the ring during relativerotational movement of the brush support and ring.

7. In the rotary contact assembly of claim 6, said electricallyconductive means comprising a hollow conductive tube.

8. In the rotary contact assembly of claim 6, said means for limitingthe penetration of the brush into said 6 opening comprising a portion ofthe brush support engaging the bend in the brush.

9. In the rotary contact assembly of claim 6, said electricallyconductive means comprising a hollow conductive tube, and said means forlimiting the penetration of the brush comprising the lip of the tubeengaging the References Cited by the Examiner UNITED STATES PATENTS2,242,273 5/1941 Taylerson 3395 2,473,526 6/1949 Hood et al. 33952,509,931 5/1950 Krantz 339-5 3,054,098 9/1962 Jacoby 339-244 X EDWARDC. ALLEN, Primary Examiner. ALFRED S. TRASK, Examiner.

6. IN A ROTARY CONTACT ASSEMBLY, A BRUSH SUPPORT, A RING HAVING ACONDUCTIVE SURFACE MOUNTED FOR RELATIVE ROTATIONAL MOVEMENT WITH RESPECTTO THE BRUSH SUPPORT, SAID BRUSH SUPPORT HAVING MEANS DEFINING ANELONGATED OPENING CONFRONTING THE RING AND CONTAINING AN ELECTRICALLYCONDUCTIVE MEANS PERMITTING ANGULAR MOVEMENT OF THE BRUSH AND MAKINGELECTRICAL CONTACT WITH THE BRUSH FOR ALL ANGULAR POSITIONS THEREOF, ARESILIENT ELECTRICALLY CONDUCTIVE BRUSH WITH ONE END THEREOF HAVING ASUBSTANTIALLY STRAIGHT PORTION, SAID BRUSH BEING OF SMALLER DIMENSIONTHAN SAID OPENING AND INSERTED LOOSELY INTO SAID OPENING IN THE BRUSHASSEMBLY AND IN ELECTRICAL ENGAGEMENT WITH SAID CONDUCTIVE MEANS, SAIDBRUSH HAVING A BEND ALONG ITS LENGTH, WITH SAID ONE END THEREOF ON ONESIDE OF THE BEND, MEANS FOR LIMITING THE PENETRATION OF THE BRUSH INTOSAID OPENING, A PORTION OF THE BRUSH ON THE OTHER SIDE OF THE BENDTANGENTIALLY ENGAGING THE RING, THE RESPECTIVE SIZE OF SAID OPENING ANDSAID BRUSH, AND THE LOCATION OF SAID OPENING IN THE BRUSH SUPPORTRELATIVE TO THE SURFACE OF THE RING BEING SUCH THAT THE BRUSH ISMAINTAINED IN CONTINUOUS CONTACT WITH THE CONDUCTIVE MEANS IN THE BRUSHSUPPORT AND WITH THE RING SOLELY BY THE OPPOSING PRESSURES ON THE BRUSHEXERTED BY THE RING AND THE BRUSH SUPPORT, WHEREBY THE BRUSH IS FREE TOSHIFT ANGULAR POSITION IN THE BRUSH SUPPORT AND MAINTAIN CONTINUOUSALIGNMENT WITH THE RING DURING RELATIVE ROTATIONAL MOVEMENT OF THE BRUSHSUPPORT AND RING.